The present invention is in the field of thermoplastic coextrusions; more particularly, the invention relates to coextrusions of thermoplastic fluoropolymers with thermoplastic polymers.
It is generally known how to coextrude film and sheet as indicated in the Modern Plastics Encyclopedia, Vol. 56, No. 10A, pp. 131-132, McGraw Hill, October, 1979. Coextruded sheet and film, are made using multimanifold dies such as a multimanifold cicular die for blown film or a coextrusion feedblock for flat cast film and sheet. The article "Trends & equipment . . . Coextrusion" by M. H. Naitove in Plastics Technology, February, 1977, pp 61-71, discussed coextrusion in further detail. For the purposes of this invention the term film includes both film and sheet unless otherwise indicated.
A variety of different thermoplastics have been coextruded to form multilayered coextruded film to take advantage of different properties in different layers. Typical multilayered coextruded film include different thermoplastic polymeric layers having specific characteristics desired in coextruded film. Coextruded films could include a layer of polyethylene or polypropylene to provide a moisture barrier. The coextruded film can incorporate a layer of ionomer or nylon to improve toughness, or a layer of nylon as an oxygen barrier. A layer of polyvinylidene chloride can be included as an oxygen and moisture barrier. A layer of ethylene vinyl acetate copolymer or an ionomer can be included to provide heat sealability to a multilayer coextruded film.
Thermoplastic fluoropolymers can be extruded or solution cast to form films. These materials offer excellent chemical resistance and barrier properties. However, fluoropolymers have not been coextruded to form multilayered film structures. This could be due to difficulty in adhering fluoropolymer film layers to other thermoplastic layers.